There is proposed a power apparatus having a tube that is restrained in its longitudinal direction and is expanded in its radial direction by charging gas, liquid, or solid material, or a mixture thereof into the tube, wherein a cylindrical sleeve that expands and contracts in the longitudinal direction and the radial direction is disposed outside the tube, both ends of the apparatus are restrained, the one of the ends of the apparatus is provided with a charging opening, and the tube is made of one of polyester-based material, polyamide-based material, polyethylene-based material, polyimide-based material, polystyrene-based material, and polycarbonate-based material, or a film or fiber having mixture thereof (patent document 1).
A motion assisting apparatus utilizing this kind of power apparatus is also proposed (patent documents 2 and 3).
In the patent document 2, the apparatus also assists a twisting motion of an elbow joint in addition to the bending and stretching motion of the elbow joint by carrying out the bending and stretching motion of the elbow joint using a joint made of elastic body.    [Patent Document 1] Japanese Patent Application Laid-open No. 2004-105263    [Patent Document 2] International Patent Application Laid-open No. 2007/043308    [Patent Document 3] Japanese Patent Application Laid-open No. 2007-167484